Information recording method and apparatus with suppressed mark edge jitters

ABSTRACT

A method for recording information is disclosed in which an information recording medium is irradiated with a recording energy beam power-modulated into at least a record power level and a record-ready power level lower than the record power level. When forming a mark portion of a predetermined length, the radiation energy of the energy beam is increased as compared with when forming a mark portion of a different length before or after the first pulse of an energy beam pulse train including at least a pulse for forming the mark portion. Also, only in the case where the energy beam is modulated by the power lower in power level than the record-ready power level after the last pulse of the energy beam pulse train including at least one pulse for forming a mark portion and the mark portion is followed by a space portion of a predetermined length, the particular radiation energy of low power level is reduced as compared with when the mark portion is followed by a space potion of a different length. The radiation energy is increased and/or decreased.

This is a continuation application of U.S. Ser. No. 10/023,719 now U.S.Pat. No. 6,529,467, filed Dec. 21, 2001, which is a continuationapplication of U.S. Ser. No. 09/773,557, filed Feb. 2, 2001, now U.S.Pat. No. 6,343,056, which is a continuation application of U.S.application Ser. No. 09/149,051, filed on Sep. 8, 1998, now U.S. Pat.No. 6,236,635.

BACKGROUND OF THE INVENTION

The present invention relates to a method and apparatus for recordinginformation in an information recording medium by radiation of an energybeam, or more in particular to an information recording method veryeffective for a phase change optical disk and an information recordingapparatus using such an information recording method.

A conventional method of recording and erasing information in arewritable record film is disclosed, for example, in JP-A-62-175948(laid open Aug. 1, 1987), which uses a magneto-optical disk of anexchange couple double-layered film as a record film. Anotherconventional method for recording and erasing information in arewritable record film is disclosed in JP-A-62-259229 (laid open Nov.11, 1987), which uses a record film for a phase change optical diskcapable of high-speed erasure by crystallization within substantiallythe same time as the laser radiation time for recording. In these cases,the power of an energy beam is alternated between at least two levelsboth higher than the read level, i.e. between at least a high powerlevel and an intermediate power level. This method has the advantagethat what is called “overwrite” is possible with new informationrecorded while at the same time erasing the existing one. Also, asdisclosed in JP-A-62-259229 described above and JP-A-3-185629 (laid openAug. 13, 1991), a record mark can be prevented from assuming a shapesuch that the rear portion of the record mark is wider than the frontportion thereof by changing the energy beam between three levelsincluding a high power level, an intermediate level and a power levellower than the intermediate level.

Research is under way for increasing the density of a rewritable digitalvideo disk (DVD-RAM) using a phase change record film. In an opticaldisk device for performing the mark edge recording in a phase changerecord film such as the DVD-RAM, substantially the same temperature andsubstantially the same cooling rate are required for recording at everypart of the outer edge where the record film is melted for forming arecord mark or a mark portion in order to prevent a mark shapedistortion and residue. The various record waveforms thus far known,however, fail to meet these conditions sufficiently and the feasiblerecording density is limited. Especially with the DVD-RAM having arecording capacity of 4.7 GB or more, the distance between centers oflaser beams radiated onto a recording medium to form adjacent two markportions thereon is small as compared with the diameter of the laserbeam spot, with the result that light is considerably overlapped indistribution. It is necessary to prevent a record mark distortion causedby this phenomenon. In the case where the space portion between markportions is short, the record mark edge position of a reproduced signalwaveform shifts due to the fact that such mark portions cannot beresolved by the beam spot. This inconvenience is also required to beprevented.

With the increase in digital signal processing rate in recent years,demand has been rising for an increased recording and reproduction rateof an information recording apparatus. In order to meet this demand, ahigher relative speed between an energy beam and an informationrecording medium has become crucial. Therefore, an information recordingmethod is required which is capable of performing a stable recordingoperation even in the case where the relative speed between an energybeam and an information recording medium is high.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an informationrecording method and apparatus capable of recording information withhigh density.

The invention is suitable for recording information accurately in thecase where the recording density is high and/or the relative speedbetween an energy beam and an information recording medium is high.

On the other hand, a technique for reducing the track pitches is underdevelopment with the intention of increasing the recording density. Amethod exists, for example, in which information is recorded in bothgrooves and lands (areas between grooves) formed on an informationrecording medium. According to this method, crosstalks of reproducedsignals from lands to grooves or from grooves to lands can be cancelledby setting the grooves to a proper depth (optical phase differencebetween lands and grooves).

The heat generated by the energy beam is used for recording information.Therefore, thermal interferences occur to adjacent tracks (groovesadjacent to lands or lands adjacent to grooves) in the case where theenergy beam position cannot be controlled in stable fashion. This leadsto the problem that the information recorded in adjacent tracks iserased.

The present invention is suitable for recording information accuratelywithout erasing the information in adjacent tracks even in the casewhere the information is recorded in an information recording mediumhaving narrow track pitches or especially an information recordingmedium corresponding to the land/groove recording scheme and in the casewhere the track pitches are not more than the diameter of the recordingenergy beam.

Another crucial problem is how to improve the recording sensitivity.Normally, with the increase in relative speed between the informationrecording medium and the energy beam, the energy beam passes a recordmark on the information recording medium within a shorter time. Thus,the amount of energy radiated on the information recording medium in aunit time is reduced, and therefore the portion of the record film to beformed with a record mark is often insufficiently heated. Also, accuraterecording, which can be accomplished with pulses of very narrow width,requires a high peak laser power.

The present invention is also suitable for recording informationaccurately without a large energy beam power in the case where therelative speed between the information recording medium and therecording energy beam is increased and/or in the case where informationis recorded in an information recording medium liable to be cooledrapidly.

According to one aspect of the invention, there is provided a method ofrecording information in a recording medium capable of being set in afirst state of a second power level and in a second state of a thirdpower level higher than the second power level of an energy beam, inwhich the energy beam is radiated while moving the energy beam and therecording medium relatively to each other and information in terms ofthe length and interval of mark portions in the second state is recordedin the recording medium, the method comprising the first step ofirradiating the recording medium with an energy beam of a first powerlevel lower than the second and third power levels before and/or afterrecording the information, the second step of irradiating the recordingmedium with at least one pulse of one or more energy beam pulses of thethird power level for forming a mark portion in the second state, andthe third step of irradiating the recording medium, before or after thefirst pulse of one or more energy beam pulses for forming the markportion, with an energy beam pulse of a radiation energy larger in thecase where the mark portion in the second state has a first length thanin the case where the mark portion in the second state has a secondlength.

In the above-mentioned method, the third step can be replaced by anequivalent third step of, in the case where the space portion followinga mark portion in the second state has a first length, irradiating therecording medium, after the last pulse of one or more energy beam pulsesfor forming the mark portion, with an energy beam pulse having an energysmaller than in the case where the space portion has a second length andat a power level lower than the second power level.

In the last-mentioned method, the two third steps can of course beemployed at the same time.

According to another aspect of the present invention, there is provideda method of recording information in the form of space and mark portionson a recording medium capable of assuming first and second physicalstates corresponding to space and mark portions of information,respectively, the recording medium being irradiated, to produce a lengthof a portion of the recording medium in the second physical state, withan energy beam being movable relative to the recording medium and beingmodulated to have power levels varying with time in a pulse waveform inaccordance with a mark portion of information, wherein:

the pulse waveform includes an information pulse section having at leastone pulse serving to form a second physical state recording mediumportion and a mark edge adjusting pulse section continuous with theinformation pulse section, the mark edge adjusting pulse section beingcooperative with the information pulse section to define the length ofthe second physical state recording medium portion to be produced.

According to still another aspect of the invention, there is provided anapparatus for recording information in a recording medium capable beingset in a first state of a second power level and in a second state of athird power level higher than the second power level of an energy beam,the apparatus comprising an energy beam radiation means and means formoving the energy beam and the recording medium relative to each other,the information being recorded on the recording medium in the form oflength and space of a mark portion in the second state, wherein theenergy beam radiation means includes a waveform generating circuithaving first means for irradiating the recording medium with a beam of afirst power level (P1) lower than the second and third power levelsbefore and/or after recording the information, second means forirradiating the recording medium with at least a pulse of one or moreenergy beam pulses of the third power level for forming a mark portionin the second state, and third means for increasing the radiation energyin the case where the mark portion in the second state has a firstlength as compared with when said mark portion in said second state hasa second length, before or after the first pulse of one or more energybeam pulses for forming the mark portion.

According to yet another aspect of the invention, there is provided anapparatus for recording information in a recording medium capable ofbeing set in a first state of a second power level and in a second stateof a third power level higher than the second power level of an energybeam, comprising energy beam radiation means and means for moving theenergy beam and the recording medium relative to each other, theinformation being recorded on the recording medium in the form of lengthand interval of a mark portion in the second state, wherein the energybeam radiation means includes a waveform generating circuit having firstmeans for irradiating the recording medium with a beam of a first powerlevel (P1) lower than the second and third power levels before and/orafter recording the information, second means for irradiating therecording medium with at least a pulse of one or more energy beam pulsesof the third power level for forming a mark portion in the second state,and third means for irradiating the recording medium, in the case wherethe space portion after a mark portion in the second state has a firstlength, with an energy smaller than when the space portion following themark portion has a second length, at a power level lower than the secondpower level after the last pulse of one or more energy beam pulses forforming the mark portion.

In this specification, at least an energy beam pulse train for forming amark portion is defined as a train of pulses for forming a mark portionarranged substantially equidistantly with a shorter interval than thechannel clock in the recording apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an example structure of a recording mediumusable by the present invention.

FIG. 2 is a block diagram showing a recording apparatus according to anembodiment of the invention.

FIG. 3 shows waveforms for explaining the information recordingaccording to the prior art.

FIGS. 4 to 7 show waveforms for explaining the information recordingaccording to other embodiments of the invention.

FIG. 8 is a diagram showing the relation between the width of a coolingpulse and the trailing edge jitter of a mark portion according to anembodiment of the invention.

FIGS. 9A, 9B, 10A, 10B show waveforms for explaining the informationrecording according to other embodiments of the invention.

FIGS. 11 and 12 show waveforms for explaining the information recordingaccording to other embodiments of the invention.

FIG. 13 is a block diagram showing an information recording apparatusaccording to an embodiment of the invention.

FIG. 14 is a block diagram showing an example of a record waveformgenerating circuit usable for the apparatus shown in FIG. 13.

FIG. 15 is a block diagram showing an example of a laser drive circuitusable for the apparatus shown in FIG. 13.

FIG. 16 shows waveforms for explaining the operation of a recordingapparatus according to an embodiment of the invention.

FIG. 17 is a diagram showing an example characteristic of asemiconductor laser usable for the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a sectional structure of a disk-shaped informationrecording medium according to an embodiment. This medium can befabricated in the following manner.

First, a polycarbonate base 12 cm in diameter and 0.6 mm in thicknesshaving tracking guide grooves for land/groove recording at pitches of0.6 μm in the surface thereof is formed with an Al₂O₃ heat diffusionlayer 12 about 30 nm thick. An 80ZnS-20SiO₂ protective layer 13 about 45nm thick is formed. A SiO₂ protective layer 14 about 5 nm thick isformed. Then, a Ge₁₄Sb₂₈Te₅₈ record film 15 about 15 nm thick and a SiO₂intermediate layer 16 about 5 nm thick are formed. Further, anabsorption difference adjusting layer 17 about 18 nm thick made of an80Mo-20SiO₂ film is formed, followed by a first reflective layer 18 of89Al-11Ti about 70 nm thick and a second reflective layer 19 of 97Al-3Tifilm about 70 nm thick, in that order. A layered film can be formed by amagnetron sputtering device. A protective film 20 is formed on theresulting assembly using an ultraviolet radiation curable resin. In thisway, a first disk member is prepared.

In exactly the same manner, a second disk member having the sameconfiguration as the first disk member is prepared. The first diskmember and the second disk member are attached to each other by the endsthereof nearer to the second reflective film through an adhesive layer,thereby fabricating a disk-shaped information recording medium.

The record film 15 of the first disk member constituting the recordingmedium fabricated in the above-mentioned way is initialized in themanner described as follows. This is exactly the case with the recordfilm of the second disk member. The description that follows, therefore,will be made only about the record film 15 of the first disk member.

The medium is rotated at a constant linear velocity of 8 m/s, and laserbeam power of 900 mW of a semiconductor laser (wavelength of about 810nm) having an elliptical spot along the radius of the medium is radiatedon the record film 15 through the polycarbonate base 11. The recordinghead is driven while automatically focusing the laser beam on the recordfilm 15. The laser beam spot is displaced by one sixteenth of the spotlength each time along the radius of the medium. In this way, the mediumis crystallized (the first physical state).

Information is recorded by an 8-16 modulated signal in a record area ofthe record film initialized in the above-mentioned manner. Therotational linear velocity of the disk is 9 m/s, the semiconductor laserwavelength is 635 nm, and the lens numerical aperture (NA) is 0.6.First, the tracking and the automatic focusing are effected with a laserbeam of a first power level P1 (1 mW) constituting a read power levelwhile radiating the disk. When the beam reaches the disk portion to berecorded in, the laser beam power is raised to a second power level forerasing the unrequired written information by crystallization. Forforming a record mark, i.e. a mark portion anew, the power is furtherraised to a third level. The record waveform for forming this recordmark (hereinafter referred to as “the mark portion”) will be describedin detail later. After a multiplicity of mark portions in amorphous orsimilar state (second physical state) are completely formed and therecord area is passed, the laser beam power is lowered to the firstpower level.

The power ratio between the third power level and the second power levelis preferably 1:0.3 to 1:0.8.

In this recording method, new information can be recorded by overwritingit directly on the old information recorded in the particular portion.In other words, an overwrite operation with a single circular light spotis possible.

There are 36 zones available for recording by the user along the radialdirection of the disk. About 25 to 60 sectors exist along thecircumference of each zone. For the record-reproduce operation, themotor is controlled by a ZCLV (Zone Constant Linear Velocity) method inwhich the rotational speed of the disk is varied from one zone toanother for recording or reproduction. In this format, therefore, thedisk linear velocity is different between the innermost circumferenceand outermost circumference in each zone.

The configuration and operation of a recording apparatus according tothis embodiment will be explained with reference to FIG. 2.

Information (digital signal) inputted from outside the recordingapparatus is transmitted to an 8-16 modulator in units of 8 bits. Inrecording the information on a disk 1, for example, 8 bits ofinformation is converted to 16 bits of information by use of a recordingmethod called the 8-16 modulation scheme. In this modulation scheme,information of 3T to 11T in mark length corresponding to 8-bitinformation is recorded on the disk (medium) 1 rotationally driven bythe motor 2. In FIG. 2, the 8-16 modulator 8 performs the modulation forthis purpose. In the foregoing description, T designates a clock periodfor information recording and is 15.6 ns in the case underconsideration. A preferable value of T in the method according to thisembodiment is in the range between 5 ns and 20 ns inclusive.

The digital signal of 3T to 11T converted by the 8-16 modulator 8 istransferred to a record waveform generating circuit 6 thereby togenerate a record waveform. The basic width of each pulse constituting apulse train of the third power level for forming a mark portion isassumed to be T or T/2, and the width of the pulse lower than the secondpower level following the pulse train, i.e. the cooling pulse width Tccan be changed from outside. The record waveform containing the pulsetrain generated by the record waveform generating circuit 6 istransferred to a laser driving circuit 7, which emits a semiconductorlaser in an optical head 3 based on the same record waveform.

In the optical head 3 mounted on the recording apparatus, the laser beamis circularly polarized. This recording apparatus corresponds to what iscalled the land/groove recording scheme in which information is recordedin both grooves and lands (areas between grooves). In this recordingapparatus, either the lands or the grooves can be arbitrarily selectedfor tracking by a land/groove servo circuit.

The recorded information can also be reproduced by use of the opticalhead. A laser beam focused to the same size as at the time of recordingis radiated on the disk, and the light reflected from the mark portionand the portion (space portion) other than the mark portion is detectedthereby to obtain a reproduced signal. The amplitude of this reproducedsignal is amplified by a pre-amplifier 4 and transferred to an 8-16demodulator 10. The 8-16 demodulator 10 converts each 16 bits into 8-bitinformation. The foregoing operation completes the reproduction of themark portion recorded.

FIG. 3 shows a well-known record waveform as a reference. FIGS. 4 to 9are diagrams for explaining record waveforms according to an embodimentof the invention. In FIG. 3, P3 designates the power of the third powerlevel capable of forming a mark portion, P2 the power of the secondpower level for achieving the crystallization of the record film of themedium, and P1 the power of the first power level for read operation.Between the pulses where a high power level is reached for forming amark portion, the power is lowered for preventing the heat accumulation.T designates the width of a channel clock. The basic width of the laserbeam pulse radiated on the medium is T/2, and the pulse interval is alsoT/2. (In FIG. 3, the width of the first pulse and the last pulse issubstantially T in the pulse train for forming a mark portion.) FIG. 3shows only the laser beam pulse waveforms for forming mark portions of3T, 4T, 6T and 11T. The mark portions of 5T to 10T, on the other hand,are formed by adding a set of waveforms including T/2 high power leveland T/2 low power level, respectively, following the first pulse of thewaveform of 4T. The mark portion of 11T, for example, is the result ofaddition of seven sets. A pulse train longer than 11T can be obtained byadding waveforms in similar fashion.

As described above, except for the waveform for the 3T mark, the widthof the first pulse of the laser beam pulse train is given as 1T, thewidth of the last pulse also as 1T, and the width of other pulses asT/2. After the last pulse of the beam pulse waveform for forming aparticular mark portion, the record film is preferably cooled bylowering the laser power to a level lower than the second power level.This pulse of low power level is called the cooling pulse. The powerlevel reached by this pulse is assumed to be a fourth power level. Alsoassume that

P1=1 mW

P2=5 mW

P3=10.5 mW

P4=0.5 mW

Then, both the leading edge jitter and the trailing edge jitterrepresent a rather satisfactory range of 20% to 25%, but a target jittervalue of not more than 10% cannot be achieved. Tc designates the widthof a cooling pulse and Po a reference power level.

The examination by the present inventors has revealed that theabove-mentioned jitters occur due to the following causes:

(1) The leading edge of the mark portion of 5T to 7T is displaced about2.0 nm (or delayed by about 2 ns in terms of electrical signal pulse)from a predetermined position in such a direction as to shorten thelength of the mark portion.

(2) The leading edge of the mark portion recorded before a short spaceportion (3T to 5T) is displaced by about 5 nm (or delayed by about 5 nsin terms of electrical signal pulse) in such a direction as to shortenthe length of the mark portion.

(3) When a 3T mark portion or a 4T mark portion is recorded, the leadingedge is shifted forward (in the direction advanced in time).

The reason why this phenomenon occurs has been vigorously studied by thepresent inventors. As a result, with a recording medium for recording(converting into amorphous state) and erasing (crystallizing) theinformation changing the phase by controlling the medium temperature totwo areas (the temperature area for crystallization and the temperaturearea of not lower than the melting point), it has been discovered that amechanism hitherto unknown works especially when recording a mark notmore than one half of the diameter of the laser beam spot. Specifically,

(1) Assume that after a first mark portion is recorded at the thirdpower level in a given position A of the medium, the center of the laserbeam is moved from position A by a distance between about one half theradius and the full radius of the laser beam spot. In the case where thesecond mark portion is recorded again at the third power level, it hasbeen found that the first mark portion is crystallized and the mark(amorphous state) disappears.

(2) The feature of the conventional waveform shown in FIG. 3 is thatwhen recording a mark portion of a length not less than 5T, the amountof energy radiation of the first pulse and the last pulse of a beampulse train for forming a mark portion is twice as large as that of thepulses held between the first and last pulses. In the record waveformfor recording 3T or 4T mark portions, therefore, the proximity betweenor integration of the first and last pulses causes an excessive amountof energy radiation, with the result that the mark portion undesirablyoutgrows a predetermined size.

(3) It is further known that a phenomenon of what is called aninter-code interference occurs in which in the case where the length ofthe shortest mark (space) portion is not more than one half of thediameter of the laser beam spot, the edge position determined by slicingthe reproduced signal of the shortest mark (space) portion interposedbetween sufficiently long space (mark) portions is considerablydifferent from the edge position determined by slicing the reproducedsignal of the shortest mark (space) portion interposed between theshortest space (mark) portions.

An object of the present invention is to predict and record thesephenomena and thereby to make possible an ultrahigh density recordingwith the length of the shortest mark (space) portion not more than onehalf the diameter of the laser beam spot.

In the energy beam pulse waveform shown in FIG. 4, the power is at thesecond level P2 of 5 mW, for example, before a mark portion is formed.When the beam reaches a position for forming a mark portion, the powerrises toward and reaches the third power level P3 of 10.5 mW, forexample. The radiation of the laser beam of the third power level meltsthe record film, which is then rapidly cooled into an amorphous state(second physical state). In order to lower the radiation energy of theenergy beam pulse waveform for recording the 3T mark portion, the laserof the 1T-wide third power level is radiated for recording.

In the case where the mark portion to be recorded is of the length of5T, 6T or 7T, the energy beam pulse waveform has a mark edge adjustingpulse before the pulse train (information pulses) for forming a markportion. Specifically, the energy beam is raised to a fifth power levelP5 0.1 mW higher than the second power level P2 before being raised tothe third power level P3. After being kept at this level for thefollowing-described time, the energy beam is raised to the third powerlevel P3. The rise of energy level (i.e. preheating) from the powerlevel P2 to power level P5 is effective as in the following case if inthe range of 0.05 mW to 2.0 mW (i.e. about 0.1% to 36.4%) when thirdpower level (P3) less second power level (P2) is 5.5 mW. The time afterreaching the fifth power level P5 before being raised to the third powerlevel is preferably 0.1T to 1.5T for the 5T mark portion, 0.1T to 2.0Tfor the 6T mark portion, and 0.1T to 1.5T for the 7T mark portion. Bysecuring these ranges, partial erasure of the mark portion by asucceeding beam pulse can be avoided. As a result, the jitter at theleading edge can be reduced to 10% or less.

Instead of changing the time after reaching the fifth power level P5before being raised to the third power level P3 according to the lengthof the mark portion, the fifth power level P5 can be changed accordingto the mark portion length within the range of power level describedabove, in such manner that P5 (6T)>P5 (5T)>P5 (7T). In this way, theleading edge jitter can be suppressed in similar fashion. The markportion length subjected to preheating is not limited to 5T, 6T, 7T butcan include 3T, 4T or 8T.

Without raising the power level as described above, as shown in FIG. 5for the 5T, 6T and 7T mark portions, the power is lowered from secondpower level P2 to sixth power level P6 with a mark edge adjusting pulseinserted following the first pulse in the energy beam pulse train(information pulse train) high in power level for forming a markportion, and after the second pulse in the same pulse train, the fourthpower level P4 is reached as a mark length adjusting pulse. When thefourth power level is 1 mW, the sixth power level P6 is raised from thefourth power level P4 by an amount between 0.05 mW and 5.0 mW inclusive.In this way, a similar effect of suppressing the leading edge isobtained. A preferred example of power difference between the sixthpower level P6 and the fourth power level P4 is 0.05 mW to 3 mW for 5Tmark, 0.10 mW to 5.0 mW for 6T mark, and 0.05 mW to 3.0 mW for 7T mark.

Reference is made to FIG. 6. The high power level that the first pulsein the energy beam pulse train (information pulse section) reaches forforming a mark portion is the third power level P3. Assume that thepower level of the second pulse to the last pulse but one in the pulsetrain is the seventh power level P7, and the power level of the lastpulse is the ninth power level P9. The third, seventh and ninth powerlevels can be the same. When the seventh power level P7 is higher thanthe third power level P3 by 0.1 mW to 2.0 mW for the level P3 being 10.5mW, however, the leading edge of the mark portion is advantageouslyprevented from growing excessively. Thus, the leading edge jitter can besuppressed to 12.5%. In the case where the ninth power level P9 is lowerthan the seventh power level P7 by 0.1 mW to 2.0 mW for the level P7being 10.5 mW, on the other hand, the leading edge jitter isadvantageously lowered. As a result, the leading edge jitter issuppressed to 12%.

Referring to FIG. 7, assume that the power level reached by loweringfrom the high power level P3 for forming a mark portion is the tenthpower level P10 different from other pulses immediately before the lastpulse and this power level P10 is raised to a level 0.1 mW to 2.0 mWhigher than the level between the second pulse and the last pulse butone, i.e. the eighth power level. Then, the leading and trailing edgejitters can be reduced. Consequently, the average jitter at the leadingand trailing edges can be suppressed to 7.5%.

In FIG. 7, at least one of the fourth, sixth, eighth and tenth powerlevels P4, P6, P8 and P10, especially, the eighth power level P8, iflower than the first power level P1 providing a read power level, can bepreferably realized simply by turning off the high frequencysuperposition of the semiconductor laser as the same amplifier outputvoltage as the first power level P1.

Trailing edge jitters are determined with the width Tc of the coolingpulse being changed at intervals of T/2 during a period from 0T to 2.5T,the cooling pulse constituting a mark edge adjusting pulse section ofthe energy pulse waveform. The energy beam pulse waveform is such asshown in FIG. 3, in which the individual power levels are: P1=1 mW, P2=5mW, P3=10.5 mW and P4=0.5 mW. FIG. 8 shows the dependency of thetrailing edge jitter on the cooling pulse width. In the case where Tc is0T, the jitter value is 18%, which changes to 8% when Tc is 1.5T. Inthis way, a superior reproduced signal can be obtained by optimizing thecooling pulse width Tc.

As shown in FIG. 9A, the cooling pulse width Tc in the energy beam pulsetrain (pulse waveform) for recording a mark portion may be made largerwhen recording information with the second shortest space portion of 4Tthan when recording information with a space portion of other lengths.Then, the shift of the edge position which otherwise might be caused bythe insufficient resolution of the beam spot is prevented and a superiorreproduced signal can be produced. For example, the cooling pulse widthTc may be 2.25 T for recording a mark portion followed by a spaceportion of 4T and may be 1.75 T, 2.00 T, 1.5T, etc. for recording a markportion followed by a space portion of another length. Then, thetrailing edge jitter will be 8%. A similar effect of trailing edgejitter suppression is obtained by setting the duration of low powerbetween 2 ns and 8 ns inclusive.

Depending on the width or the power level of the cooling pulse, the edgeposition may be controlled more sufficiently by shortening the coolingpulse width or raising the power level of the cooling pulse in the casewhere the length of the space portion is short (4T to 5T). This isbecause in the case where the cooling pulse width is sufficiently largeor the power level is sufficiently low, the preheating and hence energyruns short for recording the leading portion of a succeeding markportion. In such a case, the cooling pulse width Tc should be madeshorter when recording a mark portion followed by a space portion of 3Tto 5T than when recording a mark portion followed by a space portion of6T or more, thereby preventing jitters.

According to another aspect of the invention, the change in the shape ofmark portions before and after a space portion depending on the lengthof the space portion is compensated for in advance. Therefore, thecooling pulse information is conveniently provided in relation to thelength of the space portion. A specific example will be described below.

In the record waveform generating circuit 6 shown in FIG. 2, the 8-16modulation signal sent from the 8-16 modulator 8 is usually binarized(distinguished between “0” and “1”). Thus, a pulse train waveform forrecording the mark portion of a length corresponding to the length of“1” level on the disk 1 is generated on the one hand, and a recordwaveform for radiating the power level for crystallizing a lengthcorresponding to the length of “0” level (the length of the spaceportion) is produced on the other hand. In the process, generally, apulse train waveform corresponding to the length of each mark portion isstored in a mark table, and a pulse train waveform corresponding to thelength of the mark portion is generated. The space portion of the disk 1is irradiated with a beam of a predetermined erase power (second powerlevel).

When an attempt is made to record information using a mark table asdescribed above, the recording of a mark portion requires a mark tabledescribing combinations of the length of a mark portion to be recordedand the length of the space portions before and after the mark portion.In the presence of a mark portion and a space portion of 3T to 11T, forexample, it is necessary to store a maximum of 162 types of pulse trainwaveforms in the mark table, to determine a combination of a markportion and a space portion and to access an appropriate pulse trainwaveform from among the above-mentioned record waveforms.

In the information recording apparatus according to this embodiment, incontrast, a pulse train waveform including a pulse of third power levelcapable of recording a mark portion is generated for the mark portion,and a combination of cooling pulse power and erase power correspondingto the length of each space portion is radiated on the space portion(FIG. 9B). Specifically, a mark table and a space table are arranged inthe record waveform generating circuit 6, so that a pulse train waveformcorresponding to the length of the mark portion is called from the marktable, and a cooling pulse waveform corresponding to the length of thesucceeding space portion is called from the space table. By doing so, amulti-pulse waveform having an optimum cooling pulse is generated.

In this way, the waveforms to be stored in the mark table and the spacetable can be limited to nine types. Therefore, the record waveformgenerating circuit can be simplified, thereby contributing to a lowercost of the information recording apparatus. (This system willhereinafter be referred to as “the mark/space independent tablesystem”).

Referring to FIG. 10A, instead of changing the width of the coolingpulse of an energy beam pulse train (pulse waveform) for recording amark portion according to the length of the space portion immediatelyfollowing the mark portion, a similar effect of trailing edge jittersuppression is obtained by maintaining the cooling pulse width at aconstant level and changing the power level like P4 (3T) or P4 (4T)according to the length of the space portion immediately following themark portion. In FIG. 10A, the power level of the cooling pulse forrecording a mark portion followed by a 4T space portion is made minimum.After the end of the cooling pulse, the power is changed to the secondpower level P2. Even during the above-mentioned cooling pulse, thecrystallization occurs when the record film temperature drops to thecrystallization temperature range. After that, however, the second powerlevel P2 is held, and therefore the area having a recorded mark portionis stably crystallized into the first physical state, thus erasing theinformation stored therein. Assume that the distance between a givenmark portion and the next mark portion is small, however, e.g. that thespace portion is 3T. In the case where the second power level followingthe cooling pulse for the preceding mark portion is P2 (3T) which is 0.1mW to 1.0 mW lower than the second power level for the other marklengths, residue or shift of the leading edge of the mark portion can beprevented and the jitter of the trailing edge becomes 10%.

Also, as shown in FIG. 10B, the information recording apparatus can bereduced in cost by providing a mark table and a space table foroptimally controlling the power level of the cooling pulse according tothe mark/space independent table system.

Since the mark table and the space table are dependent on theinformation recording medium (disk), a trial write operation (theoperation of determining an optimum mark table and an optimum spacetable for each information recording medium) can be simplified byrecording an optimum mark table and an optimum space table in theinformation recording medium in advance.

The cooling rate of a rear or trailing part of a mark portion can becontrolled by changing the width or level of the low-power part (coolingpulse) following the last pulse of an energy beam pulse train forforming a mark portion and hence by changing the energy radiated on theparticular part. The shape of the mark portion can thus be optimized.

Also, if the product of the time for which the low-power part isirradiated and the relative speed between the energy beam and theinformation recording medium is not more than one third of the diameterof the energy beam spot (the distance of an area along the recordingtrack where the intensity of the energy beam is the central intensitymultiplied by exp(−2)), the distortion of the reproduced signal isreduced especially to a small value and therefore the system is mostsuitable for high density recording. In the case where the product ofthe time for which the low-power portion is irradiated and the relativespeed between the energy beam and the information recording medium isnot less than one third of the diameter of the energy beam spot, on theother hand, the erasure by the second power level (crystallization forthe phase change record film) may not be sufficiently accomplished.

FIG. 11 shows an example of a combination of the aforementioned waveformcontrol schemes.

The energy beam pulse waveforms shown in FIG. 11 have the highestpractical value among the embodiments, and can effectively suppress thejitters. In the energy beam pulse waveform used for informationrecording, a jitter value of 9% or less can be obtained by using fourpower levels including P2, P3, P4 and P5 having the above-mentionedrelation. FIG. 11 shows only the mark portions having the length of 3T,4T, 6T, 11T. In the mark portions having the length of 5T to 10T,however, a set of waveforms each having a combination of a high powerlevel pulse and a low power level pulse is added for each T/2 followingthe first pulse of the 4T waveform. The result of adding seven such setsis an energy beam pulse train for recording a mark portion having thelength of 11T. Pulses are added similarly also for the mark portionslonger than 11T. As described above, of all the pulses having asufficient energy to make an amorphous record film, i.e. the informationpulse section of the energy beam pulse waveform, the width of the firstpulse is set to 1T, the width of the last pulse to 1T and the width ofother pulses to T/2. Also, a pulse of preheat level P5 with the durationof 0 to 2T higher than P2 and lower than P3 in power level is arrangedimmediately before the first pulse of power level P3. The width of thispulse of preheat level P3 is changed in accordance with the cooling rateof the medium, the relative speed between the laser beam and the medium,the relation between the radius of the laser beam and the length of themark portion or the length of the space portion adjacent to a markportion. As an example, the conditions for the width and power level ofeach pulse are shown below. (Power level of pulse train of informationpulse section)

P2: 4.5 mW

P3: 10.5 mW

P4: 1.5 mW

P5: 4.6 mW

Width of the Cooling Pulse in the Mark Edge Adjusting Pulse Section

Width of the cooling pulse contributing to recording of a mark portionimmediately before a space portion 3T, 4T wide: 2.25T

Width of the cooling pulse contributing to recording of a mark portionimmediately before a space portion 5T wide: 2T

Width of the cooling pulse contributing to recording of a mark portionimmediately before a space portion 6 to 11T wide: 1.75T

Width of the cooling pulse contributing to recording of a mark portion3T or 4T wide immediately before each space portion: The above-mentionedwidth of cooling pulse plus 0.25T

Width of Pulse of Preheat Level P5 of Mark Edge Adjusting Section

Width of preheat pulse immediately before mark portion 6T wide: 1T

Width of preheat pulse immediately before mark portion 5T or 7T wide:0.5T

Width of preheat pulse immediately before mark portion 4T wide: 0 to1.0T (varied depending on the heat conducting characteristics of themedium)

Width of First Pulse of P3 Level in Pulse Train of Information PulseSection

Mark portion 3T wide: 1T

Mark portion 4T wide: 1.25T

Mark portion 5T to 11T wide: 1T

Width of Last Pulse of P3 Level in Pulse Train of Information PulseSection

Mark portion 3T wide: 1T (same as first pulse)

Mark portion 4T wide: 0.75T to 1T (varied depending on the heatconducting characteristics of the medium)

Mark portion 5T to 11T wide: 1T

Pulse Width of P3 Level Between First Pulse and Last Pulse

Mark portion 5T to 11T wide: 0.5T

Width of Negative-Going Pulse Between Pulses of P3 Level in Pulse Trainof Information Pulse Section

Mark portion 4T wide: 0.5 to 0.75T (varied depending on the heatconducting characteristics of the medium)

Mark portion 5T to 11T wide: 0.5T

In the case where the 8-16 random modulation signal is recorded with theabove-mentioned energy beam pulse waveform, the jitter value is 9% andremains unchanged after overwrite operation. When the cooling pulse isnarrowed by 1T or widened by 1T from the above-mentioned state, noisesoccur due to a residue at the time of overwrite operation and the jittervalue is deteriorated to 15% or more.

The waveform shown in FIG. 11 is a preferable record waveform especiallyin that the jitter level is low, the jitter is not increased even afterthe overwrite operation is repeated, and the record waveform generatingcircuit can be simplified, as described above.

Another example of combinations for waveform control is shown in FIG.12. In FIG. 12, the relative height between the third, fifth, seventhand ninth power levels is preferably as described below. The relationbetween the height of power levels and jitters is also described.

P7≧P3≧P9≧P5

Further, the relative height between the second, fourth, sixth, eighthand tenth power levels is preferably as described below.

P2>P6, P10≧P4≧P8

The relative height between the first power level and the fourth, sixth,eighth and tenth power levels is preferably as described below.

P4, P6, P10≧P1≧P8

An excessively large circuit size is avoided by assuring that the eighthpower level is the same as the tenth power level, and so is by assuringthat the seventh power level is the same as the ninth power level. It isalso possible to prevent the circuit size from increasing excessively byassuring that at least one of the sixth, eighth and tenth power levelsis the same as the fourth power level. Among the sixth, eighth and tenthpower levels, an undesirable increase of jitter due to reduction of thecircuit structure scale is small when assuring that the tenth powerlevel is the same as the fourth power level.

The above-mentioned energy beam pulse waveform can reduce the jitter(σ/Tw) by about 18% as compared with the conventional waveform shown inFIG. 3.

In the case where the width of the pulse of the pulse train of theenergy beam for forming a mark portion and the width of the coolingpulse are an integer multiple of one half of the channel clock T, thesize of the record waveform generating circuit is desirably minimized.The width of the pulse of the energy beam for forming a mark portion isnot necessarily T/2, however, but can be T/3, T/4 or an integralmultiple of the channel clock divided by an integer. In the case wherethe channel clock is divided by a greater number, the width describedabove can be desirably optimized for higher accuracy. Excessivedivision, however, undesirably increases the circuit size. A desirablecompromise, therefore, is T/2 to T/4.

The energy beam pulse waveform according to this embodiment isespecially effective when the beam spot diameter (the length along therecording track of the recording medium irradiated with the beam with anintensity at least 1/exp(2) of the intensity at the beam center) is 0.8μm to 1.3 μm and the shortest bit length is 0.25 to 0.35 μm or theshortest length of the mark portion is in the range of 0.35 μm to 0.5μm. This is by reason of the fact that as described above, depending onthe relation between the beam spot and the length of the mark portion,there is a certain range in which the preceding mark portion is liableto be erased (crystallized) by the succeeding pulse as a feature uniqueto the phase change recording scheme. This range is given by the beamdiameter and the shortest length of the mark portion. In thehigh-density recording as in the present case, the residue in the broadsense of the word has a considerable effect. Also, an especially greateffect results when the signal modulation scheme of EFM or the 8-16modulation is employed. In respect of the wavelength of the recordinglight, the range between 630 nm and 670 nm inclusive is especiallyeffective.

Although the power level of each pulse of the energy beam pulse waveformis classified into several types for convenience's sake as describedabove according to this embodiment, the pulse of each level may developan overshoot or an undershoot due to the characteristics of anelectrical signal. The effect of this invention is not lost as far as anequivalent level is secured in this range.

Also, if an optimum pulse width and an optimum power level are recordedbeforehand in a medium as the record waveform information to permit thepulse width of each power level described above to be changed inaccordance with the characteristics of the medium, a high-densityrecording is possible over a very wide range even in the case where themedium cooling rate or the linear velocity for recording (relativespeeds of the medium and the laser beam) is changed.

Unless the above-mentioned record waveform information is available, orunless the information recorded using a record waveform having thecooling pulse width determined from the record waveform information canbe normally reproduced, then a trial write operation is performed in atrial write area on the information recording medium 1. When thewaveform of FIG. 4 is used, for example, information is recorded witheach power level and pulse width as trial write parameters, and thewaveform with the smallest jitter is used as an optimum record waveform.In this way, the optimum record waveform is determined, and informationis recorded in the disk of FIG. 1. Thus, a superior reproduced signalwith a jitter of 10% or less is produced.

Also, the waveform of FIG. 5 is optimized and used for recording in amanner similar to that for the waveform of FIG. 4. A leading edge jittervalue of the signal reproduced from the information recording medium is11%. The result of a similar optimization and recording for thewaveforms of FIGS. 6 and 7 shows that the jitter values of the signalsreproduced from the information recording medium are 9% and 8.5%,respectively.

In the case where mark portions are recorded on the lands with theenergy beam pulse waveform shown in FIGS. 11 and 12 and other markportions are recorded in grooves adjacent to the lands with the energybeam pulse waveform shown in FIG. 3, the jitter value of the signalreproduced from the lands begins to be affected from the track offset ofabout 0.05 μm, and increases to 15% or more when the track offset is0.10 μm. This is caused by the phenomenon (what is called the crosserasure) in which the marks recorded on the lands are crystallized bythe heat generated when mark portions are recorded in the groovesadjacent to the lands. In the case where the mark portions are recordedin the adjacent grooves with the energy beam pulse waveform shown inFIGS. 11 and 12, in contrast, the adjacent tracks are not affected atall even when the track offset of 0.10 μm occurs. This indicates thatheat which may be excessively generated for the energy beam pulsewaveform shown in FIG. 11 or FIG. 12 (particularly their cooling pulseportions) can be suppressed by adjusting the cooling pulse width to aproper width. This energy beam pulse waveform is seen to be verysuitable for high-density recording with the track pitches not more thanthe laser beam diameter in the land/groove recording system.

The foregoing embodiments are described in detail with reference to thecase in which the cooling pulse width is 1.5T. Between 1.25T and 2.5Tinclusive, on the other hand, the cross erasure is reduced.

FIG. 13 is a block diagram showing an information recording apparatusaccording to an embodiment of the invention. An information recordingmedium 1, after being mounted, is rotated by a motor 2 at the rate of 9m/s with a constant disk linear velocity. Information on the recordabledisk linear velocity is stored together with the record waveforminformation in advance in the form of pits in the lead-in area along theinnermost circumference of the information recording medium 1. Therecordable disk linear velocity information read by an optical disk 3 istransferred to a system controller 5 through a pre-amplifier circuit 4.At the same time, information on the record waveform and the optimumrecording power are transferred to the system controller 5 through thecircuit 4. The system controller 5 controls the motor 2 based on therecordable disk linear velocity information and the radial positioninformation of the optical head 3 and rotates the information recordingmedium 1 at an appropriate rotational speed.

A record waveform generating circuit 6 has record waveforms(corresponding to, for example, the energy beam pulse waveforms shown inFIG. 12) programmed therein to meet the situation where the time widthof the fifth power level, the cooling pulse width and the time width ofthe third and ninth power levels are 0T, 0.125T, 0.25T, 0.375T, 0.5T,0.625T, 0.75T, 0.875T, 1.0T, 1.125T, 1.25T, 1.375T, 1.5T, 1.625T, 1.75T,1.875T, 2.0T, 2.125T, 2.25T, 2.375T and 2.5T. Thus, a record waveform ofa cooling pulse width suitable for the information recording medium 1can be generated based on the record waveform information transferredthrough the system controller 5. According to the record waveformtransferred from the record waveform generating circuit 6, the laserdriving circuit 7 causes the semiconductor laser in the optical head 3to emit light, so that the energy beam for recording a mark portion isradiated in a pulse waveform on the information recording medium 1.

The main operation of the information recording apparatus shown in FIG.13 will be explained with reference to FIGS. 14 to 17.

FIG. 14 is a functional block diagram showing a configuration of therecord waveform generating circuit (block 6 in FIG. 13). A clock 8fCLKeight times higher in frequency than the channel clock is supplied froma system controller (block 5 in FIG. 13) to the circuit 6. From thechannel clock 8fCLK, a clock 2fCLK twice as high as the channel clock isgenerated at a ¼ frequency division counter 6-13. Further, a ½ frequencydivision counter 6-14 generates a channel clock CHCLK. On the otherhand, the recording data input signal WTDATA from the 8-16 modulator 8is connected to the serial input terminal of a 16-bit shift register 6-1for input signal, and is shifted at the rise timing of the channel clockCHCLK. Among the parallel outputs of the shift register 6-1, the 15 bitsother than the oldest information bit are applied to a priority encoder62 for detecting the weight of “1” and an inverted priority encoder 6-3for detecting the weight of “0”. The two bits from the oldestinformation bit side, on the other hand, are applied to a decoder 6-4for detecting the boundary point between a space portion (“0”) and amark portion (“1”) and a boundary point changing from a mark portion(“1”) to a space portion (“0”). At the leading edge of the pulse atwhich the position of change to the mark portion (point where “0”changes to “1”) is detected by the decoder 6-4, the numerical value atthe point where the output of “is” to the priority encoder 6-2 isdiscontinued is stored in a first 4-bit register 6-5. The data in apreheat pattern table 6-7 and a mark pattern table 6-8 (which has two32-bit tables, though not shown) are accessed. The data thus accessedare loaded in parallel in output shift registers 6-10, 6-11 a, 6-11 b atthe trailing edge of the mark detection pulse. The serial output of thefirst output shift register 6-10 operated by the clock 8fCLK and theserial output of a second output shift register 6-11 a operated by theclock 2fCLK are converted into a first record pulse signal WRTP1-P and asecond record pulse signal WTRP2-P through AND gates 6-15 and 6-16,respectively. At the leading edge of the pulse where the decoder 6-4detects the position of change to the space portion (point where “1”changes to “0”), the numerical value at the point where the “0s”outputted to the inverted priority encoder 6-3 is discontinued is storedin a second 4-bit register 6-6. Also, at the trailing edge of the spaceportion detection pulse from the decoder 6-4, the data retrieved fromthe cooling pattern table 6-9 are loaded in parallel in a fourth outputshift register 6-12. At the same time, a serial output synchronous withthe channel clock 3N (8fCLK) eight times higher is converted into aninverted cooling pulse signal COOLP-N through a NOR gate 6-17 and a NANDgate 6-18. A write request signal (write gate signal) WRTQ-P generatedin the system controller is used as a permission signal for the ANDgates 6-15, 6-16 and the NAND gate 6-18, and the serial output of athird output shift register 6-11 b is applied as the other input signalto the NOR gate 6-17.

The above-mentioned three types of bit serial data signals WRTP2-P,WRTP1-P and COOLP-N are supplied to a laser driving circuit (block 7 ofFIG. 13, described in detail later) thereby to generate various levelsof laser driving signals. The contents of the pattern generating tables6-7, 6-8, 6-9 can be updated from time to time by data transfer from thesystem control bus 5-1 of the system controller (block 5 of FIG. 13). Asa result, it is possible to change the cooling pulse width Tc, etc.(FIGS. 11 and 12) as required.

FIG. 15 is a functional block diagram showing the laser driving circuit(block 7 of FIG. 13). This circuit includes an automatic power control(APC) circuit 7-1, three driving current superposition circuits 7-2,7-3, 7-4 and four D/A converters (DAC) 7-5, 7-6, 7-7, 7-8. The outputvalue Vr (target value of the laser power) of the APC D/A converter 7-5is set by the data transfer from the system control bus 5-1 of thesystem controller (block 5 of FIG. 13). On the other hand, the outputcurrent Ir is supplied to the semiconductor laser 3-1 to generate alaser beam, which is partially returned to a monitor photo-diode. Thus,a monitor current Ipd flows and is converted into a voltage by theoperation of a resistor R1 and an operational amplifier OPA2 (conversionvoltage=−Ipd×R1). The resulting voltage is applied through a resistor R2to an operational amplifier OPA1 and compared with the output voltage Vrof the D/A converter 5. Thus, the output current Ir is controlled insuch a manner that the output voltage of the operational amplifier OPA2(proportional to the intensity of the laser beam) is balanced with theabove-mentioned voltage Vr. The loop gain of the APC circuit isdetermined by the ratio between resistors R2 and R3, and the diode D1 isfor blocking the reverse flow of the superposition current (describedlater). In the case where the inverted cooling pulse signal COOLP-N isat high level, on the other hand, an analog switch (ASW) SW1 is closed.Under this condition, the output voltage Vm of the first currentsuperposition D/A converter 7-6 set by the data transfer from the systemcontrol bus 5-1 of the system controller (block 19 of FIG. 13) isapplied to the base of the transistor Q1. Therefore, the erase power Pm(=second power level P2) shown by equation 1 below and the superpositioncurrent ΔIm are superposed on the output current Ir.

 ΔIm=(Vcc−Vm−0.7)÷R 4  (1)

Once the inverted cooling pulse signal COOLP-N turns to low level, theanalog switch (ASW) SW1 opens. Therefore, the transistor Q1 turns offand the superposition current ΔIm ceases to flow. In similar fashion,when the first recording pulse signal (WRTP1-P) is at high level, asuperposition current ΔIh1 (the superposition current for generating thepreheat level power P5. FIGS. 1 to 4) flows. When the second recordingpulse signal (WRTP2-P) is at high level, on the other hand, asuperposition current ΔIh2 (the superposition current for generating thelaser power of third power level) flows.

FIG. 16 is a time chart showing the operation described above. Theserial signal input WTDATA representative of a record waveform and insynchronism with the channel clock CHCLK is applied to and sequentiallyshifted in the shift register SHR (6-1 in FIG. 14), so that pulseinformation corresponding to a first recording pulse signal “WRTP1-P”(output signal of the AND gate 6-15 in FIG. 14) is set (loaded inparallel) in a shift register (6-10 in FIG. 14) of a lengthcorresponding to 3T (in this embodiment, of a 24 (=8×3) bit length for aresolution of T/8) with a timing of a mark portion detection signal(“01” output of the decoder 6-4 in FIG. 14) indicating a change from aspace portion to a mark portion. At the same time, pulse informationcorresponding to a second recording pulse signal “WRTP2-P” (outputsignal of the AND gate 6-16 in FIG. 14) constituting a mark portionforming signal or an information pulse section of the energy beam pulsewaveform and pulse information corresponding to a mark portion coolingsignal (one of the input signals to the NOR gate 6-17 in FIG. 14) areindividually set in shift registers (6-11 a and 6-11 b in FIG. 14) of alength corresponding to 16T (in this embodiment, of a 32 (=2×16) bitlength for a resolution of T/2). The individually set data are thensequentially shifted to be outputted as WRTP1-P, WRTP2-P and MSHR SO-2,respectively. In a similar fashion, a space portion cooling pulseinformation is set in parallel in a shift register 6-12 of a lengthcorresponding to 3T (in this embodiment, of a 24 (=8×3) bit length for aresolution of T/8) with a timing of a space portion detection signal(“10” output of the decoder 6-4 in FIG. 14) indicating a change from amark portion to a space portion. From a NOR output of the mark portioncooling signal “MSHR SO-2” and the output of the shift register 6-12 inthe NOR gate 6-17 in FIG. 14, pulse information “COOLP-N” is obtained.These three laser drive timing signals WRTP2-P, WRTP1-P and COOLP-N areapplied to the laser driving circuit shown in FIG. 15, so that apredetermined laser driving current ILD flows to produce a laser beampower as required.

The laser driving circuit 7 shown in FIG. 15 may be partly changed insuch a manner that the used transistors are of NPN type, circuitry forusing a negative power supply is added and the above-mentioned spaceportion cooling pulse signal is applied to the added circuit. Thereby, acurrent subtraction circuit is formed, which facilitates realization ofthe waveform indicated by dotted line (laser driving current) shown inFIG. 16.

FIG. 17 is an I-P (current versus optical beam power) characteristicdiagram of a semiconductor laser (3-1 in FIG. 15) according to anembodiment of the invention. When the laser current is Ir milliamperes,the laser beam power is Pr milliwatts. Superposition of ΔIm milliampereson the current Ir leads to the laser current of Im milliamperes therebyto produce the laser beam power of Pm milliwatts (power level P2). WhenΔIh1 milliamperes is further superimposed on Im, the laser current ofIh1 milliamperes flows so that the laser beam power assumes Ph1milliwatts (power level P5). Similarly, when ΔIh2 milliamperes issuperposed on Im, the laser current of Ih2 milliamperes flows, with theresult that the laser beam power assumes Ph2 milliwatts (power levelP3).

As described above, the information recording apparatus according tothis invention comprises a record waveform generating circuit capable ofsetting and changing the preheat pulse width and the cooling pulse widthin units of T/8. Therefore, the requirement of a high disk linearvelocity is readily met. Further, a highly accurate informationrecording becomes possible in an information recording medium havingvarious cooling rates.

As an information recording apparatus, a delay circuit for delaying thetrailing edge of a pulse reaching the third power level or the coolingpulse by a predetermined amount can be inserted between the recordwaveform generating circuit 6 and the laser driving circuit 7 of FIG.13, for example, in order to adjust the mark portion edge position.

After the first pulse raised to the third power level, part of an areawhere the melting point is exceeded is liable to be cooled below themelting point, nucleated, and heated again by the succeeding pulseraised to the third power level. Thus, crystal grows, thereby oftenerasing the information. As described above in detail, however, themethod of forming a mark portion of intermediate length by first raisingpower slightly before raising it to the third power level as between 5Tand 7T or by reducing the power following the first record pulse only toa level slightly higher than the first record pulse, has the advantageof preventing the temperature drop to the nucleation temperature, thusavoiding the above-mentioned phenomenon. After the last pulse of thethird power level followed by a short space portion, the power islowered for a slightly longer time or to a slightly lower level. Thelast-mentioned method lengthens the actual succeeding space portion andreduces the adverse effect on the resolution of the beam soot especiallyin the case where the succeeding space portion is short.

Specifically, the length of the immediately-succeeding mark portion orspace portion is included in the information providing a reference fordetermining the record waveform of the presently-formed mark portion orspace portion. This is effective especially in the high-densityrecording in which a small residue (a residue in the broad sense of theword, including the effect of a previously-recorded signal pattern onthe shape of a new mark portion) has a great effect on the jitter (orshift) at the mark portion edge of the reproduced signal.

As described above, information is recorded using an energy beam pulsetrain for recording a mark portion, and the power level immediatelyfollowing the first pulse is set to not lower than the power levelimmediately following each of the other pulses. By doing so, the widthof the front part of the mark portion and the width of the rear part ofthe mark portion can be controlled independently of each other. Thismethod, therefore, is suitable for high-density recording. In the casewhere the power level immediately following the first pulse is lowerthan the power level immediately following each of the other pulses, onthe other hand, the energy amount radiated on the front part of the markportion is insufficient, and therefore the mark portion may assume theform of teardrop.

Also, in the energy beam pulse train for recording a mark portion, thepower level of the first pulse is increased as compared with the powerlevel of the last pulse, and the power level immediately following thefirst pulse is set to not less than the power level immediatelyfollowing each of the pulses other than the first pulse. In this way,the requirement for a still higher density recording is met.

Controlling the power level of the first pulse and/or the power level ofthe pulse immediately following the first pulse is effective forcontrolling the shape of the front part of the mark portion. Anespecially great effect is exhibited if this control method is combinedwith the method of controlling the radiation energy of the cooling pulseeffective for controlling the shape of the rear part of the markportion.

Further, if an information recording medium is used in which anamorphous mark portion is recorded in crystal and crystal grains largerthan those of the crystal exist around the mark portion, the width ofrecrystallized area can be easily controlled by the temperature reachedand the cooling rate. Therefore, it is difficult for the mark portion toassume the shape of teardrop or inverse teardrop, thereby making itpossible to suppress the size variations of the mark portion to aminimum. Thus, a reproduced signal faithful to the record waveform isproduced. Nevertheless, the present invention is applicable also to arecording medium of other characteristics such as the one whollyoccupied by large crystal grains.

Furthermore, since the cooling rate after recording a mark portion isdifferent between the land and groove of the recording medium, the widthof the low-power portion after the pulse train of the third power levelcan be differentiated according to whether the information is recordedin the grooves or on the lands.

Also, with the energy beam pulse train for recording a mark portion, anespecially low jitter value is obtained in the case where the energy ofthe energy beam charged in the first and last pulses is larger than theenergy charged in the other pulses. This effect is conspicuous at thetime of high-speed recording when the disk linear velocity is 9 m/s ormore or at the time of high-density recording when the length of theshortest mark portion is not more than two third of the laser beam spotdiameter.

As described in detail above, the cooling rate of the record film duringand after radiation of the energy beam for forming a mark portion can beaccurately controlled. Consequently, a medium capable of phase changebetween crystal and amorphous states (what is called a phase changerecording medium) can be used for high-density recording of information.This is due to the fact that the shape of a mark portion recorded in thephase change recording medium depends very sensitively on the coolingrate of the record film after radiation of the energy beam.

The width of the pulse in the above-mentioned energy beam pulse trainfor forming a mark portion or the width of the low-power portion(cooling pulse) following the pulse train represents the time between alocal minimum and a local maximum of the differentiation of the temporalchange of energy in the energy beam radiated on the informationrecording medium. More precisely, it represents the time between a localminimum and a local maximum of the time-differentiated signal of anoverriding electrical signal (such an electrical signal as digitized forgenerating a record waveform). In the case where the time between alocal minimum and a local maximum is quantized, the width ofquantization is called the pulse width described above. Even in thepresence of a minuscule fluctuation of the time between a local minimumand a local maximum of the temporal change of energy in the energy beamradiated on the information recording medium, the effects of theinvention are not lost if the fluctuation is one of a minor natureconsidered to be solely caused by the quantization.

The time referred to above is of course not the absolute one, but thetime relative to the clock of the highest order (the channel clock, i.e.a clock corresponding to the basic clock of the electrical signalimmediately after passing an EFM modulator, 8-16 modulator or the like).Therefore, in the case where the channel clock undergoes a change inaccordance with the relative speed between the energy beam and theinformation recording medium, the pulse width described above should bedefined taking the relation with the changed channel clock intoconsideration.

The power level described above indicates the one assumed to besustained considerably long time in each pulse (within the time betweena local minimum and a local maximum). In the case where the power levelcorresponds to the voltage level of an overriding electrical signal(such an electrical signal digitized for generating a record waveform),however, the particular correspondence is taken into account.

Also, as described with reference to the foregoing embodiment, therecording power can be prevented from increasing by recordinginformation using a waveform in which energy is distributed excessivelyto the leading part and the trailing part of the energy beam pulse trainfor recording the longest mark portion. Specifically, in the pulse trainfor forming a mark portion, the power level immediately following thefirst pulse and the power level immediately before the last pulse areincreased as compared with the power level following each of the otherpulses.

Further, in the energy beam pulse train for recording a mark portion,the power level immediately following the first pulse is set higher thanthe power level following each of the pulses other than the first andlast pulses but not higher than 200% of the second power level. Also,the shortest mark portion is recorded by two energy beam pulses, thesecond shortest mark portion is recorded by three energy beam pulses,and the third shortest mark portion is recorded by four energy beampulses. In addition, the power level between the first and second pulsesfor recording the shortest mark portion, the power level between thefirst and second pulses for recording the second shortest mark portion,the power levels between the first and second pulses and between thethird and fourth pulses for recording the third shortest mark portionare set between 50% and 170% inclusive of the second power level.

Furthermore, the power level between the second and third pulses forrecording the second shortest mark portion and the power level betweenthe second and third pulses for recording the third shortest markportion are set to not more than 50% of the second power level.

By controlling the power levels described in the above two paragraphs,it is possible to improve the recording sensitivity, and particularly,signal quality after overwriting.

An especially great effect of signal quality improvement is exhibited inthe case where in the energy beam pulse train for recording a markportion, the power level following the first pulse is higher than thepower level following each of the pulses other than the first and lastpulses but not higher than 200% of the second power level, or morepreferably, between 50% and 170% inclusive of the second power level.

Also, in the case where a mark portion of a given length is recordedwith three energy beam pulses, the power level immediately following thefirst pulse can be set to the second power level.

Further, a method considered for improving the recording sensitivityother than those mentioned above consists in increasing the width of thefirst and last pulses in the energy beam pulse train for recording atleast the longest mark portion. In such a case, however, when recordingthe shortest mark portion or the second or third shortest mark portion,the distance between the first pulse and the last pulse becomes so shortthat the energy amount radiated per unit area becomes excessive ascompared with when recording a comparatively long mark portion such asthe longest mark portion, with the result that a comparatively shortmark is liable to be long as compared with the normal length. Thisproblem is obviated by the following method. (a) At least the powerlevel of the pulse for recording the shortest mark portion is lower thanthe power level of the second pulse for recording the longest markportion, and/or: (b) At least the power level of the lowest-power one ofthe pulses for recording the shortest mark portion is lower than thepower level of the second one of the pulses for recording the longestmark portion but not lower than 75% of the power level of thelowest-power one of the pulses for recording the longest mark portion.

In the case where at least the power level for recording the shortestmark portion is lower than the power level of any one of the pulses forrecording the longest mark portion, the excessive amount of heatgenerated for recording the shortest mark portion can be reduced so thata normal length of the shortest mark portion can be secured. Further, inthe case where the power level for recording the second or thirdshortest mark portion is lower than the second power level for recordingthe longest mark portion, the excessive heat amount generated forrecording the second or third shortest mark portion can be morepreferably reduced thereby to secure a normal length of the second orthird shortest mark portion, as the case may be. In the process, assumethat the pulse level is increased with the increase of the length of themark portion to be recorded. Then, the amount of energy radiated perunit area for recording all the mark portions is averaged out, and anormal length can be secured for all the mark portions, thereby makingthis method more suitable for high-density recording.

Also, the quality of the reproduced signal is improved and the effect oflowering the power level is exhibited for recording the shortest markportion as compared with any one of the power levels for recording thelongest mark portion, in the case where the power level of the pulse forrecording the shortest mark portion is not lower than about 75% of thepower level of the lowest-power pulse for recording the longest markportion. An especially great effect is produced when the power level forrecording the shortest mark portion is between 85% and 95% inclusive ofthe power level of the second pulse for recording the longest markportion. On the other hand, the effect of the invention is not producedin the case where the power level for recording the shortest markportion is lower than 75% of the power level of the second pulse forrecording the longest mark portion.

In the energy beam pulse train for recording a mark portion, the widthof the first and last pulses reaching the third power level is increasedas compared with the width of those other than the first and last pulsesreaching the third power level, and at least the power level of thepulse for recording the shortest mark portion is set lower than thepower level of the second pulse for recording the longest mark portion.By using such a waveform, the recording sensitivity is improved and asuperior recording operation can be performed.

Also, the cooling pulse can be arranged after other power levels or, forexample, the second power level for a short time, instead of immediatelyfollowing the last pulse in an energy beam pulse train for recording amark portion.

What is claimed is:
 1. A method of recording information in a recordingmedium capable of being set in a first state with an energy beam at afirst power level and in a second state with an energy beam at a secondpower level higher than said first power level, said energy beam andsaid recording medium being moved relatively to each other whileradiating said energy beam on said recording medium thereby to recordinformation on said recording medium, the method comprising: afterirradiation of said recording medium with an energy beam at said firstpower level, irradiating said recording medium with an energy beam pulseat said second power level, wherein a duration of said irradiation withsaid energy beam at said first power level is changed in accordance witha relative speed between said energy beam and said recording medium. 2.An information recording method according to claim 1, wherein said firststate is a crystallized state, and said second state is an amorphousstate.
 3. An information recording method according to claim 1, whereinsaid recording medium is further irradiated with an energy beam at athird power level lower than said first power level in such a mannerthat said recording medium is irradiated with energy beams at saidsecond power level and said third power level alternately, therebyforming a mark portion on said recording medium.